It is well known in the prior art to add surfactants to alkaline developing compositions. For example it is known from EP 099 003 and EP 134 407 to use an anionic surfactant in a developer that has a pH of from 8 to 12, wherein the surfactant is added to stabilize the solution at low temperature.
According to EP 366 321 a surfactant is added to prevent overdevelopment of positive working compositions, which surfactant may be non-ionic such as polyoxyethylene lauryl ether or an ethylene oxide/propylene oxide condensate of poly(ethylene)glycol; the latter being prefered since it also prevents soiling deposits being formed on the plate surface when developing radiation sensitive plates in some automatic plate processors using hard water in their plate washing section. The pH of the developer is not given explicitely.
From EP 720 060 it is known to use one or more surfactant to adjust the surface tension and thereby allow a fast wetting of the sensitive layer, in particular when spraying the developer on the plate. Cationic, anionic, betainic and non-ionic surfactants, alone or in combination, are disclosed to be suitable therefore without further specification. EP 720 060 is related to alkaline developers, but the pH is not explicitely disclosed.
Aqueous alkaline developing solutions are known from EP 732 628, that comprise a non-ionic surfactant and at least another surfactant selected from anionic or amphoteric surfactants. Said developing solutions allow a reduced amount of sludge and less foam.
According to EP 992 854 an amphoteric and at least one anionic surfactant are used together with an N-alkoxylated amine in an alkaline aqueous developer concentrate. Said developer concentrate makes a developer possible having a high development capacity and a reduced tendency of forming unwanted depositions on the developed plates and in the processing apparatus. The amphoteric surfactant disclosed in EP 992 854 preferably is an aminoacid, a salt thereof or an alkylamidoalkylbetain and the anionic surfactants preferably are C2- to C16-alkyl or aryl sulfates. In addition, the concentrate of EP 992 854 can further contain ingredients like non-inonic and cationic surfactants. The addition of N-alkoxylated amines has the tendency to increase the turbidity of the resulting developers. Thus these developers can give increased settlement, which reduces the circulation in the processor. The consequence is a continuous reduction of circulation flow during usage, which finally can end up in a blockage of processors's spray bars. On the other hand most of the settlements remain in the processor and need to be removed at the end using special cleaning agents.
There still is a demanding need to further reduce depositions in the developing apparatus and on the processed printing plates, especially during long run processing. Moreover, the sedimentation stability of used developers is unsatisfactory for known compositions, what is problematic in batch processing with long dwell times between said batches.
The depositions when using a developer according to the state of the art are formed from already detached components of the layer, that are unsufficiently dissolved or dispergated and are deposited on the recording material again or are carried into downstream stations (washbath, gumming station) of the developing machine. Already developed recording materials may become useless in this way. It is mainly during development in machines that components of the layer which are contained in the developer in the form of cakes, filaments or pigment residues, are deposited on the printing plates. In addition, such depositions are formed in the developing machine reducing the circulation flow and decreasing the efficiency of processing, whereby the cleaning effort at the end is high and often aggressive cleaning agents have to be used.